This circuit emits an audible signal when the mains voltage ceases. The circuit is from a 1973 publication. The pair of transistors can be BC548 and BC558 and the touch time depends on capacitor C2.

This circuit emits an audible signal when the mains voltage ceases. The circuit is from a 1973 publication. The pair of transistors can be BC548 and BC558 and the touch time depends on capacitor C2.